JPS60157375A - Halftone expressing system - Google Patents

Abstract

PURPOSE:To prevent monotonous repetition of picture element patterns and to improve its picture quality by determining the kind and number of dots that constitute picture elements according to the density of halftone, and changing arrangement of dots by comparing these values with peripheral dots. CONSTITUTION:Picture signals made to signals after reading an original picture are compared with the threshold value of 2X2-matrix ternary dither in a comparator circuit 1 and stored in a memory 2. Two continous rasters of the bit information stored in the memory 2 are selected alternately by a selector 3 and transferred to a register 4 as 2-bit information of dot. Transferred information is sent to a relational operating circuit 8 in unit of 8 bits, and the relational arithmetic circuit 8 judges whether 2X2-matrices watched presently and past two matrices in the direction of main and sub-scanning are the same or not. The result of judgement is sent to a CPU9. In response to this result, the CPU9 changes arrangement of dot pattern of 2X2-materices.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application) The present invention relates to an apparatus for expressing halftones using a pixel pattern composed of a plurality of dots.

(Prior Art) Conventionally, as a halftone expression method, there is a method of expressing halftones by repeating p of a pixel pattern composed of a plurality of dots. In this method, when a wide halftone pattern of a certain density is recorded, the halftone of the wide pattern is reproduced by repeatedly displaying a uniquely determined pixel pattern nine times.

As an example of this, an intermediate iii stable development method using a ternary dither method will be described. Now, considering the ternary dither method that can record three levels of 0, 1/2 and 1 level, the ternary dither method can record the density of the read pixel of interest.
Ilj, the display level is Plj, the threshold matrix between the levels from 0 to 1/2 is asj + the threshold matrix between the levels from 1/2 to 1 is bij, then these relationships can be expressed as follows. This is what I did.

According to this ternary dither method, the threshold, value matrix a1j
By appropriately changing l bB , the contrast density of the recorded image can be changed.

FIG. 1 shows a pixel pattern expressing a certain halftone using a ternary dither method 2×2 matrix, and FIG. 2 shows a halftone of a single-density wide pattern expressed using the pixel pattern. As is clear from FIG. 2, the halftone is composed of two different vertical lines A and B. Line A is a line represented by dots of Lebel density, and line B is a line created by alternately combining dots of 0 and 1/2 levels.

The intermediate tone of the wide pattern represented by these two vertical lines A and B can be visually perceived as a repetition of the two lines A and H, and is the intermediate tone of the wide pattern with a single density. There was a problem with not being able to get into tune.

These problems apply not only to halftone expression of a wide pattern with a single density, but also to halftone expression when the density changes over a small pattern width.

As described above, the conventional halftone expression method has the disadvantage that clear halftones cannot be reproduced.

(Objective) The object of the present invention is to eliminate the drawbacks of the prior art as described above, and to achieve
An object of the present invention is to prevent monotonous repetition of pixel patterns in a device that expresses halftones, improve image quality, and provide excellent image quality.

(Summary) A feature of the present invention is that in a method for expressing halftones in which one pixel is composed of a plurality of dots, the S type and number of dots constituting a pixel are determined according to the halftone density. means,
means for comparing the dot arrangement determined by the means with the dot arrangement of surrounding pixels, and means for changing the dot arrangement when the dot arrangement is the same as the dot arrangement of the surrounding pixels; The key point is that the image is expressed using .

(Example) The present invention will be explained below using examples. Figure 3 shows
An example in which the present invention is applied to a transfer type thermal recording device will be shown. This device follows the ternary dither method, 2×27) I
It is assumed that it is possible to express intermediate tones using J-X.

An image signal obtained by reading an original image is compared with a threshold value of a 2×2 matrix ternary dither in a comparator circuit 1, and is stored in a memory 2. The memory 2 has a capacity to store bit information of two or more rasters.

By the way, in the 2×2 matrix ternary dither method, there are three types: full dot (.), half dot (.), and no printing. These 3SD pixels are each 11. 01
．． When expressed as 2-bit information of 00, each dot (pixel) of the original image information has 2-bit information. Therefore, 1
Assuming that the raster is composed of N dots (pixels),
One raster is represented by 2N bits. In addition, a 2×2 matrix can be represented by two consecutive rasters, and furthermore,
It is expressed in 8 bits.

For example, if the output of the comparator l is as shown in FIG. 4(a) for the first and second rasters, the two dots of the first raster and The two dots of the second raster constitute a 2×2 matrix. Also, if we express this in terms of the value of l1x11, θ″, we get
It is represented as bl in the same figure. As is clear from this figure, a 2×2 matrix is expressed in 8 bits.

In this way, in the comparator circuit 1, the dots printed for each rask are converted into the values of 1'' and ``0'' of 2x2Y), and are stored one by one in the memory 2 for every two stars. Raster alternately 1.2, 1.2...
. . . and transfer the 2-bit information of the dot to the register 4.

Then, 8-bit matrix information is created for each 2×2 matrix. For example, in the example of FIG. 4 fbl, 01, 00, 11 . Register 4 in the order of 01
is stored in

1st. The second and third 2-in buffers 5, 6°7 are
Each has a capacity of 2×2N bits.

The current data stored in the register 4 is sent to the comparator circuit 8 in 8-bit units (one 2×2 matrix unit).
and is sent to the CPU9.

Let this 8-bit unit information of interest be LIJ (where l indicates a value in the main scanning direction, and j indicates a value in the sub-scanning direction).

In addition, the comparison calculation circuit 8 has the following characteristics: °2×
2 matrix in the main scanning direction (i.e., Ll
j-++, Llj-s) is the third line buffer 7
Furthermore, the past two in the sub-scanning direction (ie, Lj-4a, jLi-5j) are input from the first and second line buffers 5 and 6, respectively. In the comparison calculation circuit 8, the currently focused 2×2 matrix Li
3 and the said Lord and! 11 scanning directions each past 2
three matrices, namely Ltj−” rLij +
+ It is determined whether Li-*j and Li-1j are the same. Then, the judgment result passes through line X,
Input to CPU9.

Here, one specific example of the comparison calculation circuit 8 will be explained with reference to FIG. As is clear from FIG. 5, in the comparison calculation circuit 8, each of the 8 bits of the 2×2 matrix Llj of interest is input to one input terminal.

Eight exclusive OR circuits 8a1, 8a2 . to which 8 bits of the past 2x2 matrix are input are input to the other input terminal.・
・・・・・・・・・8a8 and the result is ・NOR gate sb, sb, which takes NOR using two adjacent bits.
b.

It is composed of 8bi l and 8b4.

For example, the exclusive OR circuit 811. ~8. When the 8-bit information of Llj is inputted from the register 4 to one input terminal of , and the 8-bit information of Li-1j is inputted from the second line buffer 6 to the other input terminal,
Data corresponding to the bits shown in the figure are input to the respective input terminals of the exclusive OR gates 1188&, -8, and 8. Of course, as the past 2x2 matrix to be compared, the 2x2 matrix Ll-1j from the first line buffer 5 + the 2x2 matrix Llj-1゜Llj-t from the third line buffer is input. , compared with the 2×2 matrix Iqj, which is currently attracting attention.

Next, the operation of the comparison calculation circuit 8 will be explained. Now, it is assumed that the pixel pattern of the 2×2 matrix Ll-1j two rasters before in the sub-scanning direction and the pixel pattern of the 2×2 matrix Lij of the raster of interest at present are as shown in FIG. Then, each input of the exclusive OR circuits 8a8 to 8.8 of the comparison operation circuit becomes as shown in Table 1.

1st group - Also, each output of the NOR gates 8b1 to 8b becomes 1@order 1, 0, 1.1. According to this specific example.

When the output of NOR gates 8b1 to 8b4 is 1, 2X2
It will be clear that 0 indicates the presence of dots of the same density at corresponding positions in the matrix, while 0 indicates the presence of dots of different densities.

In this way, a 4-bit comparison result can be obtained by comparing the currently focused 2x2 matrix with one past 2x2 matrix. In this embodiment, one matrix of interest is compared with four surrounding matrices, so a total of 16 bits of comparison information is obtained.

This 16-bit comparison information passes through line
sent to. The CPU 9 detects how many 1's there are among this 16-bit comparison information, and if, for example, l is 8 or more, that is, more than half, it rotates the 8-bit information of the attention matrix input from the register 4 by 2 bits. do.

For example, in the above example, the attention matrix I4j is 00
(Since it is jllol, it is rotated by 2 bits to become 01000111. Then, this is stored in a predetermined position of the third 2-in buffer 7 from the CPU 9 via the 2-in y. In this way, If there are 8 or more 1's out of 16 bits, it means that more than half of the same dot patterns were present in the past four matrices, so if you rotate the focused matrix Llj'E2 bits, the combination of dot patterns will change. , it is possible to reduce the degree of matching of dot patterns.

As described above, the bit information of the 2×2 matrix of the raster of interest is determined and stored in the third line buffer 7. Once the bit information for one raster is determined, it is transferred to the memory 10a and the first 2-in buffer 5. At the same time, the bit information stored in the first line buffer 5 is transferred to the second line buffer 6.

The thermal head drive circuit 11 drives the thermal head 12 using a well-known method based on information stored in the memory 10. As a result, the ink donor film 13
is selectively heated, and the image is transferred to the recording paper 14.

As described above, according to this embodiment, the 2×2 matrix of the raster of interest is compared with the past two 2×2 matrices in each of the main scanning direction and the sub-scanning direction,
It is possible to change the arrangement of the dot patterns of the 2×2 matrix currently being focused on so that the dot patterns forming these matrices do not match as much as possible.

Therefore, it is possible to prevent halftones from being expressed by monotonous repetition of pixel patterns, and to improve image quality.

Note that in the above example, the similarity of one focused matrix with four surrounding matrices was examined, so 16
Bit comparison information was obtained. K, which reduces the information amount of this comparison information, can be calculated by taking the logical product of the corresponding information in each of the comparison information with the past two in the main scanning direction and the comparison information with the past two in the sub-scanning direction, for a total of 8 It can be shortened to bit comparison information.

In addition, in the embodiment described in -1, if 8 bits or more of the 16 bits of comparison information are 1'', the 2X2 matrix Llj currently being focused on in CPTJ9 is rotated by 2 bits, but if 8 bits or more Of course, it is not limited to , and can be set arbitrarily.

Furthermore, although the above embodiment has been described as an example in which halftones are expressed using a 3I* dither method 2×2 matrix, the present invention is not limited to this, and any pixel pattern composed of a plurality of dots may be used. Application is possible.

Moreover, although the number of past matrices to be compared is two in each of the main and sub-scanning directions, it may be two or more or one.

Furthermore, the present invention is not limited to transfer-type thermal recording devices, but can also be applied to recording systems that digitize and handle image signals, such as direct thermal recording, electrostatic recording, inkjet recording, and laser recording. can do. The present invention can also be applied to halftone expression in color displays.

(Effects) According to the present invention, the probability that a matrix consisting of the same dot pattern exists in the vicinity of the matrix of interest in the main and sub-scanning directions is reduced, so that monotonous repetition of pixel patterns is prevented. Therefore, the image quality is improved, and even better image quality can be provided.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a 2x2 matrix for the ternary dither method; Figure 2 is a diagram representing halftones using a 2x2 matrix;
FIG. 3 is a block diagram of one embodiment of the present invention, and FIG. 4 is a block diagram of an embodiment of the present invention.
5 is a circuit diagram showing a specific example of the comparison circuit shown in FIG. 3, and FIG. 6 is a diagram showing a specific example of the output information of the comparison circuit shown in FIG. It is a figure which shows an example of matrix L1j. 1'... Comparison circuit, 2... Memory, 3... Selector, 4... Register, 5, 6.7... 1st. Second. 3rd line buffer, 8... comparison calculation circuit,
9...CPU, 10...Memory, 11...Thermal head drive circuit attorney Michi Hiraki Li j Patent Application No. 58-241635, March 3, 1985 2, Name of the invention Halftone expression method 5 Person making the amendment 5, Claims of the specification to be amended 1 Detailed description of the invention, drawings Brief explanation column and drawing 6, contents of amendment (1) #J1 detailed document page 3! Corrected "two" in line 15 to "two concentrations." (2) On page 4, line 10, "sharp" was corrected to "sloping". (3) Lines 3 to 5 of the same page 5 [one pixel...four phases...pixels according to]" has been changed to "one pixel pattern is composed of multiple dots, and the pixel pattern is used as a unit to form a pixel. In a method that expresses intermediate tones, the pixel pattern is corrected according to the intensity of the read image signal. (4) Delete “Yazu” in line 6 of the same page. (5) Corrected "pixel" in lines 7, 8, and 9 of the same page to "pixel pattern." (6) Page 6, line 5, line 12, line 13, line 15, line 18, page 7, line 1, line 2, page 8, lines 1-2, page 12 Lines 13 and 15, page 13, line 9, "raster" is corrected to "scanning line". (7) On page 6, line #117, “comparator” was changed to “comparison circuit”
and correction. (8) Page 7, lines 7-11 “Print for each rask...
Select ・・・・・・・・・・・・ and correct it as follows. ``Each draft of the original image information read out for each scanning line is converted into a 2-bit value of %1 1%O', and is stored one by one in the memory 2 for each scanning line. 2-bit information of the first dot of the first scanning line, 2-bit information of the first dot of the second scanning line, 2-bit information of the second dot of the first scanning line, and 2-bit information of the second dot of the first scanning line are alternately displayed on two consecutive scanning lines. 2-bit information of the second dot of the line, ・・・・・・・・・・・・・・・
(9) On the same page, line lK13, ``and......'' is selected, and then one 2 x 2 matrix pixel pattern shown in Fig. 4(a) is selected. "With Ak" and corrected. 6 o'clock 8th j [Correction of 3rd line "unit" to "pixel pattern unit". ONE In the 5th and 6th lines of the same page, "i indicates a value." [1 is the number of the 2x2 matrix pixel pattern in the sub-scanning direction, and j is the main pixel pattern of the same pixel pattern. Indicates the number in the scanning direction. ” and corrected. (b) In lines 8 and 10 of the same page, “past 2” was replaced with “past 2”.
``matrix information'' and correction. 2) Page 10, line 3, F and Comparison J were corrected to ``compared sequentially with 1 or in parallel.'' a◆ Correct the "r dot pattern" on page 13 of the same cylinder, line 12, to "pixel pattern". (2) Correct "dot pattern of matrix" in lines 16 to 14 of the same page to "dot of matrix pixel pattern". (2) Correct the ``r dot pattern'' on the 15th line, line 10 of the same page with the ``pixel pattern J.
x2 matrix" to r2x22x2 matrix turn"
and correction. 6 → Amend the claims as shown in the attached sheet. (To) Amend Figure 4 of the drawing as shown in the attached sheet. 2. Claims (1) In a system for expressing halftones by forming an image using elementary patterns as units, where elementary patterns are composed of a plurality of dots. +! Means for determining the m class of dots constituting a pixel pattern according to the intensity [k of the taken image signal, means for comparing the dot arrangement determined by the means with the dot arrangement of surrounding pixel patterns, and surrounding pixels. This halftone expression method is characterized in that it is provided with a means for changing the dot arrangement when it is the same as the dot arrangement of the pattern, and the image is expressed by the dot arrangement of 84 dots and the dot arrangement of the surrounding pixel pattern. (2) A patented halftone expression method characterized in that the above-mentioned halftone expression is a transfer type thermal recording method. Figure 4

Claims (2)

[Claims] (1) In a method in which one pixel is composed of a plurality of dots to reproduce an intermediate value, a means for determining the type and number of dots constituting a pixel according to the halftone density, and a method for determining the type and number of dots constituting a pixel according to the halftone density; means for comparing the dot arrangement with the dot arrangement of surrounding pixels, and means for changing the dot arrangement when the dot arrangement is the same as that of the surrounding pixels, so that the image is expressed with a dot arrangement different from that of the surrounding pixels. The intermediate 1Ii1 expression method is characterized by the following. (2) A patented halftone expression method characterized in that the above halftone expression is a transfer type thermal recording method.